1. Field of the Invention
The present invention relates to a method for driving a flat panel display, and more particularly to a method for driving an organic electro-luminescent (EL) panel display such that it improves an image quality and an effective lifetime of the organic EL panel display.
2. Discussion of the Related Art
Generally, the organic EL display electrically excites a fluorescent organic compound, such that it emits light. The organic EL display drives N×M organic EL cells using a voltage or current signal, such that it displays a desired image.
A conventional organic EL display will hereinafter be described with reference to FIG. 1.
FIG. 1 is a structural diagram illustrating a conventional organic EL display.
Referring to FIG. 1, the conventional organic EL display cell includes an anode composed of an ITO, an organic thin film, and a cathode layer composed of a metal.
The organic thin film is configured in the form of a multi-layered structure, which includes an Emitting Layer (EML), an Electron Transport Layer (ETL), and a Hole Transport Layer (HTL), such that it improves light-emitting efficiency due to the balancing of electrons and holes. Also, the organic thin film further includes an Electron Injecting Layer (EIL) and a Hole Injecting Layer (HIL).
The above-mentioned organic EL cell is classified into a Passive Matrix (PM)—based organic EL cell and an Active Matrix (AM)—based organic EL cell. The PM-based organic EL cell forms an anode and a cathode orthogonal to each other according to an addressing scheme, and selects a desired line, such that it is driven. The AM-based organic EL cell connects a Thin Film Transistor (TFT) and a capacitor to each ITO pixel electrode, and maintains a voltage by capacitance, such that it is driven.
The PM-based organic EL cell or the AM-based organic EL cell is classified into a voltage-write scheme and a current-write scheme according to the type (i.e., voltage or current) of a signal received from a drive circuit.
FIG. 2 is a circuit diagram illustrating a pixel structure of a conventional AM-OLED (Organic Light Emitting Diode) panel. FIG. 2 is a conventional AM voltage-write pixel circuit for driving an OLED using the TFT, and shows a representative example of N×M pixels.
Referring to FIG. 2, a current-drive-type transistor (Mb) is connected to the OLED, such that a current signal for emitting the light is written in the OLED.
In this case, the current capacity of the current-drive-type transistor (Mb) is controlled by a data voltage received via a switching transistor (Ma). In order to maintain the data voltage during a predetermined period of time, the capacitor is connected between a source and a gate of the current-drive-type transistor (Mb).
The N-th selection signal line (Select[n]) is connected to the gate of the switching transistor (Ma), and a data line (Data[m]) is connected to the source of the switching transistor (Ma).
Operations of the pixel having the above-mentioned structure will hereinafter be described with reference to FIG. 2.
If the switching transistor (Ma) is switched on by the selection signal (Select[n]) applied to the gate of the switching transistor (Ma), a data voltage (V DATA) is applied to a gate (Node A) of the drive-type transistor (Mb) via the data line.
In response to the data voltage (V DATA) applied to the Node A, the current signal is written in the OLED via the drive-type transistor (Mb), resulting in the implementation of the light-emitting operation.
The conventional method for driving the OLED having the above-mentioned structure may unexpectedly change the brightness between pixels due to a threshold-voltage deviation and a mobility deviation of the drive-type transistor, such that it may unavoidably deteriorate uniformity of a display screen.
Also, due to the power (P=I*V) consumed by the pixel and the heat generated by the power, the drive-type transistor and the OLED are deteriorated, and their lifetimes are reduced, such that it is difficult for the conventional OLED to be made commercially available.